1) Field of the Invention
The present invention relates to a technique for acquiring organism characteristic data from organism information such as, for example, a fingerprint, a palmar pattern, a blood vessel pattern (fundus retina vasoganglion, vein vasoganglion) and an iris muscle pattern and particularly to a technique for acquiring organism characteristic data (fingerprint data or ridge structure data including characteristic point information) necessary for personal identification and so forth from a plurality of partial images (fingerprint images) sampled successively, for example, while a finger is moved with respect to a sensor face in a sweep type fingerprint sensor.
2) Description of the Related Art
With improvement in function in recent years, small-size information apparatus such as a portable telephone set and a PDA (Personal Digital Assistant) now allow connection to a network and storage of a great amount of personal information and so forth. Therefore, a demand for improvement in the security performance in apparatus of the type just mentioned is increasing significantly.
In order to assure the security in apparatus of the type mentioned, personal identification based on a password, an ID (IDentification) card and so forth conventionally used commonly can be adopted. However, the password and the ID card have a high degree of possibility of misappropriation. Therefore, it is much demanded to achieve personal identification (identification for certifying that a user of an apparatus is the one registered in advance) having a high degree of reliability. Personal identification based on organism information (biometrics information) has a high degree of reliability. Therefore, it is considered that the personal identification just described can satisfy the demand described above. Particularly, where a fingerprint is used as the organism information, not only the reliability but also the convenience are high.
Where personal identification is performed using a fingerprint as organism information, a capacitance type fingerprint sensor or an optical type fingerprint sensor is used to sample a fingerprint (a pattern formed from ridges which may contact with a sensor face of the fingerprint sensor and groove lines which do not contact with the sensor face) as image information from a finger of an object person of the authentication. Thereafter, characteristic information (for example, position information of a branch point or an end point) is extracted from a foreground of the fingerprint image (for example, a ridge image). Then, the extracted characteristic information and registration characteristic information of the object person of the authentication registered in advance are collated with each other. Thus, decision whether or not the object person of the authentication is the original person, that is, the personal identification, is performed.
Incidentally, a general fingerprint sensor (plane type fingerprint sensor) for sampling a fingerprint image from an object person of authentication normally has a sensor face having a size greater than that of a finger. However, in recent years, in order to incorporate a fingerprint sensor into small-size information apparatus such as a portable telephone set and a PDA, such a method as described below is utilized. In particular, the sensor face is formed smaller than that of a finger and a plurality of partial images sampled through the sensor face are synthesized to obtain an image of an entire fingerprint.
As a fingerprint sensor which can deal with the situation just described, a sweep type fingerprint sensor is available. The sweep type fingerprint sensor has a rectangular sensor face (image pickup face) having a length and an area sufficiently smaller than those of a finger. It is to be noted that, relative movement of a finger with respect to a sensor face is hereafter referred to as “sweep”.
Where the sweep type fingerprint sensor is used, a plurality of partial images of a fingerprint are successively sampled by the fingerprint sensor while the finger is moved with respect to the sensor face or the sensor face (fingerprint sensor) is moved with respect to the finger. Then, an entire fingerprint image (a full image) is reconstructed based on a plurality of thus sampled partial images (refer to Japanese Patent Laid-Open No. 91769/1998).
In particular, if the sweep type fingerprint sensor is used, then, for example, a great number of rectangular fingerprint partial images as shown in FIG. 24 can be picked up. Conventionally (according to a system disclosed in Japanese Patent Laid-Open No. 91769/1998), in order to perform personal identification using the fingerprint partial images, the fingerprint partial images are synthesized as shown in FIG. 25 to form a single entire fingerprint image (called full image in Japanese Patent Laid-Open No. 91769/1998). Thereafter, the personal identification is performed using a method similar to that used for fingerprint identification performed using the plane type fingerprint sensor. In particular, referring to FIG. 26, a plurality of fingerprint partial images 1 to n are connected to each other (step S1), and image processes such as a binarization process and a thinning process are performed for the reconstructed entire fingerprint image (step S2). Then, information of a characteristic point (minutia; a branch point or an end point of a ridge) is extracted and produced as organism characteristic data from the entire fingerprint image after the image process is performed (step S3), and personal identification is performed based on the extracted fingerprint data.
It is to be noted that, in FIG. 25, an arrow mark V1 indicates a vector which indicates a relative positional relationship between a first fingerprint partial image and a second fingerprint partial image. Further, another arrow mark V2 indicates a vector which indicates a relative positional relationship between the second fingerprint partial image and a third fingerprint partial image.
However, as described above, the conventional technique that a plurality of rectangular fingerprint partial images are synthesized with each other to produce a single entire fingerprint image and the image processes are performed for the entire fingerprint image and then organism characteristic data is extracted from the image for which the image processes have been performed to perform personal identification have the following two subjects (1) and (2).
(1) After a plurality of rectangular fingerprint partial images are synthesized with each other to produce an entire fingerprint image, the image processes and organism characteristic data extraction process are performed. Therefore, a memory capacity for storing at least an entire fingerprint image is required. Actually, when various processes are performed for an entire fingerprint image, the entire fingerprint image must be copied. Therefore, a memory capacity equal to two or three times the data amount of the entire fingerprint image is required.
(2) The image processes, organism characteristic data extraction process and personal identification process (collation process of fingerprint data) described above are started after sliding movement of a finger on the sweep type fingerprint sensor is completed. This is because an entire fingerprint image can be produced only after the finger is slidably moved to the last end and a plurality of rectangular fingerprint partial images which cover the entire fingerprint are acquired. Therefore, while a finger is slidably moved on the sweep type fingerprint sensor, even if a CPU is idle, the various processes described above cannot be assigned to the CPU.